<!DOCTYPE html>
<html>
<head>
    <!-- 页面meta -->
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>传智健康</title>
    <meta name="description" content="传智健康">
    <meta name="keywords" content="传智健康">


</head>
<body class="hold-transition">
<select name="cars" id="aa">
    <option value="volvo">Volvo</option>
    <option value="saab">Saab</option>
</select>
<input type="button" value="ok" onclick="f()"/>

</body>
<script>
    function f() {

        va=document.getElementById("aa");
        alert(va.value);
        var btn=document.createElement("option");
        var t=document.createTextNode("000");
        btn.appendChild(t);
        va.appendChild(btn)
    }
</script>
</html>
